The author is a Forbes contributor. The opinions expressed are those of the writer.

Loading ...

Loading ...

This story appears in the {{article.article.magazine.pretty_date}} issue of {{article.article.magazine.pubName}}. Subscribe

A study completed by scientists at the US Food and Drug Adminstration (FDA) may have identified one of the weaknesses in our vaccine defense against pertussis.

Study author Jason Warfel and colleagues at the US FDA used baboons to examine how protective the acellular pertussis vaccine really is, having replaced the very-effective whole-cell vaccines of yesteryear following concerns about side effects from the latter. Hints in other studies--including findings in recent pertussis outbreaks suggesting that specific vaccinated age cohorts were experiencing faster-than-expected waning immunity--led to this baboon investigation. The authors looked at how well vaccinated baboons were protected from transmitting pertussis to other baboons. They found that although baboons receiving the acellular vaccine didn't experience severe pertussis symptoms when exposed to the disease, they did contract it and could pass it to others.

Although this work was in baboons and baboons aren't people, it provides compelling evidence for what many experts suspected: Acellular pertussis vaccine just isn't very good at preventing pertussis transmission. It can keep a baboon--and maybe a person--from feeling sick, but doesn't keep them from being infected and passing the infection along.

When the original whole-cell pertussis vaccine emerged in the mid-20th century, rates of pertussis plummeted. And even before the acellular vaccine was introduced, outbreaks started cropping up. Because rates really kicked up after the acellular version came on the scene, though, one hypothesis has been that this vaccine just isn't as effective and doesn't confer immunity for as long as the whole cell version or a native infection. This work with baboons supports that idea and carries it a step further: Because the current vaccine appears to suppress symptoms, vaccinated but infected people can be carriers of pertussis without knowing it and thus unwittingly pass it on in the community. The original vaccine trials, the authors note, didn't screen vaccinated participants who were symptom free for infection and thus overlooked this possibility.

Newborns are especially susceptible to terrible outcomes from pertussis, and a common practice is "cocooning," or ensuring that anyone in contact with an infant has had a pertussis booster. This work calls into question reliance on this practice, given that an asymptomatic person could still pass the infection on to others. The authors comment on this in their paper, but hasten to add that

it is important to note that our data in combination with human data show that vaccination with aP provides excellent protection from severe pertussis. Therefore, any short-term plan for addressing the resurgence of pertussis should include continued efforts to enhance aP (acellular pertussis) immunization. However, to protect the most vulnerable members of the population and achieve optimal herd immunity, it will be necessary to develop a vaccination strategy that effectively blocks pertussis infection and transmission.

In an interview with NBC News, one of the authors, Tod Merkel of the FDA, also noted that even though cocooning doesn't seem terribly effective, it's "better than nothing":

An infected person with a cough is probably spreading more germs that someone who spreads it through talking or exhaling.

And having the vaccine, it seems, still protects against a severity of symptoms that are the hallmark of pertussis, otherwise known as the 100-day cough that makes you vomit.